Recent studies have concluded that surface coal mine drilling presents
a serious risk of silicosis to drillers and driller helpers, indeed most
of the recent case reports on silicosis in rock drillers involve surface
coal mine drillers. Traditionally rock drillers in underground coal mines
were thought to be at risk of silicosis.

Surface Mining Process

An early step in the surface or strip mining process is the removal
of topsoil and other overburden materials, including sandstones, shales,
limestones, and unconsolidated soils. Removal of these materials may require
drilling holes into the rock formation to accept explosive charges for
blasting. After blasting, the debris is cleared with earth?moving equipment
such as drag line cranes, end loaders, or power shovels.

Silica Exposure During Surface Mine Drilling

When the drilled rock has significant crystalline silica content, the
drill operators and helpers may be exposed to large amounts of respirable
crystalline silica. Such exposure places these workers at high risk of
developing silicosis. Rock drillers operate large, mobile rotary rigs that
drill holes in the rock.

Rock drillers working at surface and underground mines are covered by
Mine Safety and Health Administration regulations. Nonmining hard rock
drillers are covered by Occupational Safety and Health Administration regulations.

The National Institute for Occupational Safety and Health described
23 cases of silicosis from exposure to crystalline silica during rock drilling.
Of the 23 workers reported, 2 workers have already died from the disease,
and the remaining 21 may die eventually from silicosis or its complications.

Case No. 1 Acute Silicosis.

A 33 year old male quarry rock driller developed respiratory symptoms
in August 1986 after working in Pennsylvania surface coal mines since 1975.
A chest X ray in August 1986 showed relatively minor abnormalities, but
the worker's symptoms improved and he continued to work.

In May 1987, the driller's respiratory symptoms returned along with
severe weight loss, fevers, night sweats, joint pain, reduced lung function,
swollen lymph nodes, and progressive worsening of his chest X?ray. Antibiotics
did not improve his condition, and open lung biopsies confirmed acute silicosis.

After treatment with high dose corticosteroids and antituberculosis
drugs, the driller stabilized and improved slightly until February 1990,
when his condition deteriorated. He died of progressive respiratory failure
from silicosis in September 1991.

The driller reported that most of the drilling he did before 1983 involved
wet techniques to suppress dust. Thereafter he drilled without dust suppression
measures and without a respirator, even though the dust was sometimes so
thick that he "couldn't see anything."

Case No. 2 -Acute and Accelerated Silicosis

In April 1979, a 34 year old male rotary driller reported a 6-month
history of shortness of breath, dry cough, weight loss, and pale skin color
in body extremities. For the preceding 5 years, this worker had operated
a rotary drill at a surface coal mine using dry drilling methods.

Examination revealed increased heart and breathing rates, abnormal lung
sounds, healed ulcers on the fingertips, reduced lung function, and abnormal
chest X rays. Open lung biopsy confirmed acute silicosis. Although the
patient was treated with aggressive therapy for 8 months, lung function
continued to deteriorate and the patient died of respiratory failure in
June 1981.

Discovery of this case of acute silicosis led to a medical survey of
nine other drillers who worked for the same company. Two of the workers,
aged 28 and 31, had accelerated silicosis and had been drillers for fewer
than 6 years. Exposure concentrations are unknown because the crystalline
silica content was not measured in the coal dust samples collected during
the years 1972. However, much of the rock encountered by the drillers was
sandstone, which is likely to have had a high crystalline silica content.

Case No. 3 Accelerated and Chronic Silicosis

Seven cases of silicosis in surface miners were reported from a single
hospital in West Virginia during the period 1978-88. All cases were in
men aged 25 to 51 who were involved with surface drilling for 3 to 19 years.

Five of the drillers suffered from accelerated silicosis: one was infected
with Mycobacterium tuberculosis, one had a positive tuberculin skin test
without proven active infection, and one had progressive massive fibrosis
(a condition in which large areas of lung tissue become scarred and collapse).
The other two drillers suffered from chronic silicosis. Both were in advanced
stages of the disease, including progressive massive fibrosis.

Case No. 4--Chronic Silicosis

A survey of 18 caisson drilling sites in Hong Kong identified 12 cases
of chronic silicosis among 118 workers exposed to high concentrations of
silica. Six of these workers also had active cases of tuberculosis. All
12 workers had 10 to 20 years of occupational exposure.

Site visits showed little evidence of attempts to control dust at the
source. For example, dust suppression measures were not used with pneumatic
tools, and exhaust ventilation was not supplied in the shafts. In deeper
caissons, fresh air was usually supplied by a compressor through a makeshift
duct, but the blowing increased airborne dust concentrations. Some dust
was suppressed by the natural seepage of water at the bottom of the excavation,
and workers at some sites routinely wet the work face to suppress dust.

In the past, reusable cloth masks were commonly used at caisson drilling
sites. More recently, however, workers have provided their own particulate
filter masks.

Conclusions

The cases of silicosis described in the case studies illustrate the
risk of serious or fatal illness in rock drillers and the conditions that
favor the development of silicosis. These conditions are as follows:

The presence of respirable crystalline silica dust

Inadequate dust control measures

Inadequate respiratory protection

The absence of adequate medical screening and monitoring programs

The absence of adequate air monitoring programs for respirable dust

The National Institute for Occupational Safety and Health recommends
the following measures to reduce crystalline silica exposures in the workplace
and prevent silicosis and silicosis related deaths:

1.Before mining begins, assess the potential for exposing workers to
crystalline silica during removal of the overburden.

2.Conduct air monitoring to measure worker exposures.

3.Use control measures such as wet drilling and exhaust ventilation
to minimize exposures.

7.Provide periodic medical examinations for all workers who may be exposed
to crystalline silica.

8.Post signs to warn workers about the hazard and to inform them about
required protective equipment.

9.Provide workers with training that includes information about health
effects, work practices, and protective equipment for crystalline silica.

10.Report all cases of silicosis to State health departments and to
OSHA or MSHA.

Engineering Controls

Effective source control measures and good work practices should be
implemented to minimize worker exposure to crystalline silica. Examples
of control measures include dust suppression skirts, wet drilling, local
exhaust ventilation, and isolation of the worker in enclosed drilling rig
cabs with positive pressure air conditioning.

Personal Hygiene

The following personal hygiene practices are important elements of any
program for protecting workers from exposure to crystalline silica:

All drillers should wash their hands and faces before eating, drinking,
or smoking.

Workers should not eat, drink, or use tobacco products in the drilling
area.

Workers should shower before leaving the work site.

Workers should park their cars where they will not be contaminated with
silica.

Protective Clothing

The following measures should be taken to assure that the drillers'
dusty clothes do not contaminate cars, homes, or work sites other than
the drilling area:

Workers should change into disposable or washable work clothes at the
work site.

Workers should change into clean clothes before leaving the work site.

Respiratory Protection

Respirators should not be used as the only means of preventing or minimizing
exposures to airborne contaminants. Effective source controls such as dust?suppression
skirts, wet drilling, enclosed cabs, local exhaust ventilation, and good
work practices should be implemented to minimize worker exposure to silica
dust. The National Institute for Occupational Safety and Health prefers
such measures as the primary means of protecting workers. However, when
silica source controls cannot keep exposures below the National Institute
for Occupational Safety and Health safety standards, controls should be
supplemented with the use of respiratory protection during rock drilling
operations.

When respirators are used, the employer must establish a comprehensive
respiratory protection program as outlined in the National Institute for
Occupational Safety and Health Guide to Industrial Respiratory Protection
and as required in the OSHA respiratory protection standard and in the
MSHA standards. Important elements of these standards are an evaluation
of the worker's ability to perform the work while wearing a respirator,
regular training of personnel, periodic environmental monitoring, respirator
fit testing, maintenance, inspection, cleaning, and storage, and selection
of proper respirators.